1. Field of the Invention
The invention relates to a method and device for microfiltration, ultrafiltration, pervaporation or reverse osmosis of suspensions, emulsions or for gas separation where the material to be filtered is passed through a tubular wire membrane where the established pores between adjacent membrane windings are adjustable.
2. Description of the Prior Art
Processes and filter devices for microfiltration of particles from suspensions or gases utilizing a tubular wire wound membrane are known. In these existing processes and devices the membrane windings are wound under pre-stress and the slit-like membrane pores between adjacent membrane windings provide the separation of the particles to be filtered out of the feed. Such procedures for microfiltration, however, typically do not permit the separation of particles for ultrafiltration, pervaporation or gas/gas separation.
German Patent No. DE-OS 38 17 578 discloses a process and a device for micro and ultrafiltration as well as for reverse osmosis In this process, a membrane preferably is utilized that is formed by a tubular body wound with wire under pre-stress. The membrane can be coated with a moderately elastic, stretchable material coat that reduces the pore size. This membrane is used in a filtration device. The filtration process can be performed in a flow-through procedure or in a cross current effect as well as in the Daaden procedure.
German Patent No. DE-PS 35 22 725 discloses a membrane that is spirally formed of wire with or without pre-stress that has a material coat. This material coat can be applied before or after the winding process and can consist of fine organic or inorganic particles. With their crystalline or grid-like structures and their gaps, these can exert increased filter effects appropriate for special applications. The particles can be graphite, graphite oxide, metal, metal oxide, ceramic or other particles which are applied to the wires or fibers either by themselves or with a carrier substance (suspension, e.g., of water, fat, oil) and subsequently anchored tightly to the membrane The filter effect of these particles is generated by their porosity. The disadvantage of such membranes is their expensive production. Furthermore, since the particles are anchored tightly to the membrane, there is a danger that the entrances of the pores are plugged by this material coat during filtration and that a back-flow cleaning is difficult to accomplish. Additionally, the particles used for the material coat are only effective due to the entrances formed by them, i.e., the resulting porosity, and not due to other effects, such as an affinity to certain substances.
The present invention is designed to clearly reduce the separating borders of these known filter membranes in a simple manner so that the size of the particles to be separated from a feed can reach up to the ultra range (mol. separating area) and pervaporation as well as gas/gas separation can be provided, if necessary, by the use of composite membranes or separating membranes.
This invention also provides the advantage that the size of the pores between adjacent windings of a tubular membrane of a filtering device can be decreased in a direct manner through a reduction of the winding distances and by insertion of a fine separating layer. This results in the ability to reach the ultrafiltration range and to perform pervaporation as well as gas/gas separation. Thus, the fine separating layer functions as filter, phase and gas separating element, while the tubular membrane essentially serves as a support with microfiltration characteristics for the continued fine separating layer. Therefore, the diameter of the wire for the membrane windings can be large. The application of high filtration pressures and the achievement of high filter efficiency become possible. The fine separating layers are made of substances that exist in the feed or that are added to it during filtration. Because of the cross current effect, these substances are guided to the pores for forming the fine separating layer. The fine separating layer is maintained in the form of loose substances by the cross current effect, possibly with a continual exchange of substances. The fine separating layer can be porous or transport active depending on the substances used.